Electrical vacuum discharge device



Dec. 24, 1929. A. P. H. s. NICKEL- ET AL 1,740,700

ELECTRICAL VACUUM DISCHARGE DEVICE Original Filed Feb. 24. 1927 [72 van Ions:

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Patented Dec. 24,1929

UNITED STATES.

PATENT OFFICE ALBERT PAUL HANS-GER?!) NICKEL, OF GHARLOT'I'ENBURG, AND JOHANNES J'OACHm SPANNER, OF BERLIN, GERMANY ELECTRICAL VACUUM DISCHARGE DEVICE Application filed February 24, 1927, Serial No. 170,679, and in Germany August 1, 1924. Renewed March 14, 1929. 1

Our invention relates to improvements in electrical vacuum discharge devices, such for example as radio tubes. In a divisional application, filed March 14, 1929, Serial No. 347,042, we are claiming the tube in association with apparatus for operation, and are there claiming the method of operation; in this application we claim the tube and its structure. As is known to those skilled in the art in discharge tubes provided with glowing cathodes the space charge is neutralized by positive ions, which ions are produced within the tube by ionizing metal or gas atoms contained within the tube colliding with electrons. By the action of the anode field the positive ions move in the direction of the said field and in opposition to the electron cloud surrounding the glowing cathode, thus neutralizing the space charge. By the positive ions an impulse is imparted to the electrons towards the anode, whereby the action of the anode field is assisted, and the tube may be operated with a smaller anode voltage. We have discovered that under definite conditions this fact can be used for controlling the current of electrons emanating from the cathode. Our invention is based on the discovery that not only the electrons, but also the positive ions are afl'ected by the oscillations of the potential difference existing between the cathode and the grid, and that the said ions are thrown in a greater or smaller degree, according to the said oscillations, into the electron cloud surrounding the cathode, so that they affect the current of electrons emanating from the cathode in dependence of the said oscillations. Therefore, while in tubes now in use the said oscillations act only directly on the electrons, they have, in our improved tube, an additional indirect action through the intermediary of the positive ions. Now, the said indirect action is considerably more eifective than the direct action on the electrons, because the positive ions can be brought into closer proximity to the electrons forming the space charge, than the grid. As is known to those skilled in theart, in order to have a high action, the grid should be placed as near as possible to the glowing cathode, and, for technical reasons, the said distance cannot be reduced beyond a certain limit. However, the ions having the action of a non-mechanical grid, are not subjected to the said limitation.

We have found that the controlling effect on the positive ions is not obtained under any circumstances in a practically valuable degree, but only in such cases in which definite conditions are maintained. Though positive ion currents the intensity of which to that of the electron currents is at a ratio less than 1: 10000 have a certain small controlling eflect, yet the said controlling effect attains a practical value only, if the volumetric densities (that is the number of the atoms multiplied by the atomic weight of the atoms) of the positive ions and the electrons adapted to be affected thereby are substantially alike, which is the case, if the tube is filled for example with hydrogen gas at a pressure of about 1/2000 to 1/10000 millimeter column of mercury. In this case, when applying normal voltages to the electrons, a light-bluish and distinctly bounded aureole is formed by the glowing discharge, which aureole appears close to the inner and outer sides of the anode cylinder. Thus the said aureole is the criterion showing whether or not the vacuum within the tube satisfies the above condition, while the figures have not yet been scientifically ascertained with absolute exactness.

In order to illustrate the invention in a diagrammatical way we have shown our improved tube and the said aureole of the glowing discharge together with a diagram in the accompanying drawing, in which Fig. l, is a sectional elevation showing the vacuum tube,

Fig. 2, is an elevation showing the vacuum tube and the action of the positive ions on the negative electrons in a diagrammatical way, and

Fig. 3, is an elevation showing a tube which is partly coated with metal and partly transparent.

In Fig. 1 we have shown a cathode tube the general construction of which is known in the art, which however, contains a filling of hydrogen, metal vapor, or a mixture of both,

at a pressure of about 1/2000 millimeter column of mercury. The tube comprises a glowing cathode 3, a grid 4 and an anode 5.

The correct pressure of the gas is ascertained in the operation of the tube from a small and distinctly bounded aureole developed around the cylindrical anode 5, the said aureole having been indicated in the figure in dotted lines.

The controlling effect will be best understood from the diagram shown in Fig. 2. By the potential difference between the anode 5 and the cathode 3 the positive ions are moved towards the cathode, where they have been indicated by signs, and they remove electrons indicated in the figure by signs from the space charge, the number of the electrons thus removed being several hundred times larger than that of the positive ions. The current of the electrons towards the anode is in part directly affected by the potential difference between the cathode 3 and thegrid 4. However, the said potential difi'erence between the cathode and the grid also acts on the current of the positive ions towards the cathode, so that the electron current is further affected by the positive ions according to the action of the potential difference on the ions.

So far it has been assumed that the gas or metal atoms necessary for producing the ions are brought into the tube from without and in the course of the manufacture thereof. However, the filling may also be produced by vaporizing or decomposing suitable bodies on a suitable part of the tube, for example on a platinum wire or the glowing cathode. For producing ions adapted to control the emission of electrons substances of two different kinds may be used for generating ions If it is desired to intensify comparatively slow oscillations we prefer to operate with ions having a large mass and the velocity of which within the electric field is small. Such ions are produced for example from compounds of the heavy lead, for example sulfate of lead (PbSO a large amount of the said compound being needed for the reason that the consumption thereof by generation of ions is comparatively large in view of the large molecular volume. By reason of the small velocity of the said ions the current of ions is small. But if it is desired to intensify rapid oscillations and, at the same time, to reduce the consumption of the compound producing the ions we prefer to coat the wire or the glowing cathode with compounds of lithium, kalium or natrium for example oxide of lithium (Li O), or compounds of beryllium, which compounds develop light positive ions. In both cases the volumetric density (that is the number of the atoms multiplied by the atomic weight of the atoms) of the currents of ions must be substantially the same as thatofthe electron currents to be controlled, in

order that the indirect action of the potential difference between the grid and the cathode on the current of electrons be practically important.

Hydrogen has a function similar to that of the said light metals. It is located in the same group of the periodic system of the elements. Probably the said hydrogen is even preferable by reason of its small atomic weight. A

The indirect controlling of the current of electrons is particularly effective if the positive ions are generated on the glowing cathode itself from which the electrons are emitted. For this purpose we provide the glowing cathode with a double coating one adapted to emit electrons, for example CaO, and the other one adapted to emit ions, for example PbSO or we make use of a metal compound, such for example asone of the pure hydrogen compounds of the alkali or earth alkali metals, preferably calcium hydrid (CaH which compounds are slowly decomposed into their components at the temperatures at which electrons are emitted (900 abs). Upon emission of electrons the positiveions fall directly into the negative potential maximum generated by the cloud of electrons surrounding the cathode (space charge). If now a potential difference produced between the grid and the cathode acts on the said positive ions thrown into the space charge, the said ions which are in close proximity to the glowing cathode, have a strong influence on the electrons, because the average velocity of the electrons within the space charge is substantially zero. Therefore, the electrons are induced more or less to leave the space charge. Thus they affect the current of electrons in accordance with the oscillations of the potential difference between the grid and the cathode.

The vaporization of metal atoms within the tube tends to reduce the gas pressure, so that the tube becomes hard. Now, in order to maintain the gas pressure, it is necessary, more particularly in glass tubes having a coating of magnesium, zinc or aluminum, to charge the said metallic coating with a gas of the character of the gas used for filling the tube. For this purpose we apply the metals in a state of fine distribution on the inner wall of the glass receptacle while the tube is filled with gas. If now the tube is operated the absorbed gas is gradually set free so as to prevent hardening. For the same purpose suitable bodies such as mica or coal may be placed into the tube either separately or in connection with the metal coating, which bodies are capable of absorbing the gas in the course of the manufacture ofthe tube. In the preferred construction we make use of a small plate of mica for absorbing the gas, which plate is placed on the inner wall of the tube while applying the metal coating thereto, so that no metal is applied to the portion means of of the wall covered thereby. Afterwards the said plate falls away from the wall of the tube and to another part of the tube, so that the tube can be inspected through the said non-coated portion of the wall.

The gas pressure may be further regulated by physically or chemically saturating the said inner part of the tube with gas so that an equilibrium is produced between the gas pressure within the tube and that within the said inner part, in which case a transmission of gas from the inner part to the tube takes place only when the gas pressure within the tube has been reduced and the equilibrium disturbed.

For producing the said equilibrium, we proceed as follows: The said inner part of the tube, say the anode or a special electrode, is first completely saturated with the gas, for example hydrogen. Thereafter the said anode is mounted in the tube, and heated for a definite period of time and at a known temperature while removing the gas set free by a vacuum pump. The temperature and the period of time can not be determined beforehand, but it depends on the velocity of the evacuation by means of the pump, and it a tube having a filling of gas, a cathode, an anode, and a grid, said cathode being coated with a hydrid of an alkaline earth metal adapted at the temperature of the emission of electrons to be slowly decomposed into its components.

4. A vacuum discharge device comprising a tube having a filling of gas, a cathode, an anode, and a grid, said cathode being coated with hydrid of calcium.

In testimony whereof we hereunto afiix out signatures.

. ALBERT PAUL HANS-GERD NICKEL.

JOHANNES JOACHIM SPANNER.

must be ascertained by experiment, which may be done, for example, by evacuating a suitable number of tubes difierent periods of time and at difierenttemperatures, and ascertaining what tubes are not changed as to their vacuum after very long operation. In such tubes the temperatures and periods of time have been correct, so that the figures thus obtained can be used in the manufacture of other tubes of the same construction.

In Fig. 3 we have shown a discharge tube of this type. The main portion 6 of the glass wall of the said tube is internally coated with metal, while at the top of the said wall a portion 7 is not coated.

Instead of usin positive ions for indirectly controlling t e current of electrons we may use negative ions. Such negative ions are roduced for example by vaporization within the tube of .iodin compounds or by filling the tube with iodin vapor.

We-claim:

1. A vacuum discharge device comprising a tube having a filling of as, a cathode, an anode, and a grid, said cat ode being coated with an ion-emitting metal compound other than the constituents of the tube-filling gas, the gas pressure within the said tube being such that by ionization of the gas a distinctly bounded gleam is produced near the anode. r t

2. A vacuum discharge device comprising a tube having a filling of as, a cathode, an anode, and a rid, said cat ode being coated with a hydri of a suitable metal adapted at the temperature of the emission of electrons to be slowly decomposed into its components.

3. A vacuum discharge device comprising 

